<!doctype html>
<html>
  <head>
    <title>Dragover repeating</title>
    <style type="text/css">
div:first-child {
  height: 100px;
  width: 100px;
  background: orange;
  display: inline-block;
}
div:first-child + div {
  height: 100px;
  width: 100px;
  background: blue;
  display: inline-block;
}
    </style>
    <script type="text/javascript">
window.onload = function () {
  var numsecs = 5, maxpolltime = 0.550, minpolltime = 0.150;
  var blue = document.getElementsByTagName('div')[1], p = document.getElementsByTagName('p')[0];
  var numfired = 0, readytocount = false;
  document.getElementsByTagName('div')[0].ondragstart = function (e) {
    e.dataTransfer.effectAllowed = 'all';
    e.dataTransfer.setData('text','dummy text');
  };
  blue.ondrop = function (e) {
    e.preventDefault();
  };
  blue.ondragover = function (e) {
    e.preventDefault();
    if( readytocount ) { numfired++; }
  };
  blue.ondragenter = function (e) {
    e.preventDefault();
    p.innerHTML = 'Keep the mouse perfectly still...';
    //give the tester a second to get ready
    setTimeout(function () {
      readytocount = true;
      numfired = 0;
      p.innerHTML = 'Keep the mouse perfectly still for '+numsecs+' seconds';
      var countsecs = numsecs;
      var intr = setInterval(function () {
        countsecs--;
        if( countsecs ) {
          p.innerHTML = 'Keep the mouse perfectly still for '+countsecs+' seconds';
        } else {
          clearInterval(intr);
          var passed = numfired >= Math.floor( numsecs / maxpolltime ) && numfired <= Math.floor( numsecs / minpolltime );
          document.getElementsByTagName('p')[0].innerHTML = ( passed ? 'PASS' : 'FAIL' ) +
            '<br><br>(Fired ' + numfired + ' times in ' + numsecs + ' seconds, must be between ' +
            Math.floor( numsecs / maxpolltime ) + ' and ' + Math.floor( numsecs / minpolltime ) + ')<br>You can release the drag now';
        }
      },1000);
    },1000);
  };
};
    </script>
  </head>
  <body>

    <div draggable="true"></div>
    <div></div>
    <p>Drag the orange square over the blue square, then keep the mouse perfectly still until the result appears.</p>
    <noscript><p>Enable JavaScript and reload</p></noscript>

  </body>
</html>
